Many studies have been done to show before and after results with rehab for patellofemoral pain syndrome (PFPS). They look at the position of the kneecap (patella) in the groove where it tracks up and down. Some studies have found mild improvement after treatment. But other studies have shown that X-ray alignment was the same between the painful and pain free knees.
In fact patients with severe joint changes on X-ray may get better with treatment while patients with mild changes don't.
What researchers have found is that patients who get better have improved muscle strength and flexibility. They used a combination of rest, ice, and activity to get better. Exercises to restore normal timing of contraction seemed to help. Rehab to improve joint position sense called proprioception is also important.